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United States Patent |
5,131,025
|
Hamasaki
|
July 14, 1992
|
Intelligent modem system which determines proper access thereto
Abstract
An intelligent modem system which is used for connecting an information
processing terminal such as a microcomputer with a public communication
line by modulating and demodulating the data transmitted between the
information processing terminal and the public communication line,
comprising: an information set up circuit which can set up at least ID
information; and a reception operation control circuit which verifies if
an incoming call is from an authorized party or not by responding to the
public communication line according to the ID information, and connects a
modem circuit connected to the public communication line to a line leading
to the information processing terminal only when an incoming call is
confirmed to be from an authorized party. Thereby, the information
processing terminal connected to the modem system may not be equipped with
an arrangement to identify the other parties of communication whereby the
cost for software for the information processing terminal may be reduced,
and, when an attempt is made by an unauthorized party to get access to the
modem system, the information processing terminal may continue the
execution of the current jobs without being disrupted by any such
unauthorized incoming calls.
Inventors:
|
Hamasaki; Hideyasu (Kawaguchi, JP)
|
Assignee:
|
Omron Tateisi Electronics Co. (Kyoto, JP)
|
Appl. No.:
|
561253 |
Filed:
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July 30, 1990 |
Foreign Application Priority Data
| Nov 25, 1987[JP] | 62-297102 |
Current U.S. Class: |
379/93.02; 375/222; 380/266; 713/164; 713/184 |
Intern'l Class: |
H04M 011/00 |
Field of Search: |
379/95,97,98
380/23,25
375/8
340/825.52
|
References Cited
U.S. Patent Documents
3984637 | Oct., 1976 | Caudill et al. | 379/95.
|
4246442 | Jan., 1981 | Hashimoto | 379/95.
|
4310720 | Jan., 1982 | Check, Jr. | 379/95.
|
4430728 | Feb., 1984 | Beitel et al. | 379/95.
|
4484307 | Nov., 1984 | Kulczyckyj et al. | 379/95.
|
4520233 | May., 1985 | Smith | 379/95.
|
4546213 | Oct., 1985 | Dick | 379/95.
|
4596021 | Jun., 1986 | Carter et al. | 379/98.
|
4601011 | Jul., 1986 | Grynberg | 379/95.
|
4604499 | Aug., 1986 | Hughes | 379/95.
|
4626623 | Dec., 1986 | Lahaye | 379/95.
|
4679226 | Jul., 1987 | Muehleisen | 379/95.
|
4685124 | Aug., 1987 | Smitt et al. | 379/95.
|
4782498 | Nov., 1988 | Copeland, III | 375/8.
|
4831648 | May., 1989 | Nishino | 379/95.
|
4905281 | Feb., 1990 | Surjaatmadja et al. | 379/95.
|
Primary Examiner: Dwyer; James L.
Assistant Examiner: Chan; Wing F.
Attorney, Agent or Firm: Dickstein, Shapiro & Morin
Parent Case Text
This application is a continuation, of application Ser. No. 07/275 127,
filed Nov. 22, 1988, now abandoned.
Claims
What we claim is:
1. An intelligent modem system for connection between an information
processing terminal and a public communication line comprising:
means for storing at least an identification code in said modem system;
means for providing a detection signal when an incoming call from a calling
remote party is detected on said communication line;
a modem circuit for modulating data sent to said communication line and
demodulating data received from said communication line; and
reception operation control means for verifying during a connection period
when a calling remote party is communicating with said modem system over
said public communication line that said remote party is authorized to
communication with said information processing terminal and comprising:
means responsive to said detection signal for answering an incoming call on
said communication line and for operating said modem circuit to establish
a data communication connection with said calling remote party;
means operative after said data communications connection is established
and during said connection period for verifying that an identification
code received from said calling remote party bears a correspondence to
said stored identification code;
means for starting a continuous transmission of data to said calling remote
party after said identification code has been verified;
means for discontinuing said continuous transmission of data upon receiving
a continuous transmission of data from said calling remote party; and
means for connecting said information processing terminal with said modem
circuit during said connection period to enable communications between
said terminal and said calling remote party through said modem circuit
only when said received identification code is verified and said
continuous transmission of data has been discontinued by said means for
discontinuing said continuous transmission of data.
2. An intelligent modem system as in claim 1 further comprising
transmission operation control means for self-introducing said modem
system to a called remote party, said transmission operation control means
comprising:
means for connecting said modem circuit to said communication line;
means for initiating a call to said called remote party over said
communication line;
means for sending said identification code to said called remote party; and
means for connecting said information processing terminal to said modem
circuit to enable communications between said terminal and said called
remote party through said moden circuit only upon receiving permission to
do so from said called remote party.
3. An intelligent modem system as in claim 2 wherein said transmission
operation control means further comprises:
means for determining if said called remote party has been designated as
having means to identify said called remote party; and
means permitting said self-introduction by said transmission operation
control means only when said called remote party is equipped with means to
identify it.
4. An intelligent modem system as in claim 1, further comprising means to
disconnect said modem system from said public communication line when said
calling remote party is not an authorized party.
5. An intelligent modem system as defined in claim 2, wherein said
reception operation control means further comprises:
a) means for sending out a carrier to said calling remote party after
connection of said modem system to said public communication line in
response to the presence of said detection signal;
b) means for receiving said identification code transmitted from said
calling remote party;
c) means for comparing said received identification code with said stored
identification code;
d) means for starting a continuous transmission of data to said calling
remote party when said received identification code agrees with said
stored identification code;
e) means for connecting said modem circuit connected with said public
communication line to a line leading to said information processing
terminal in synchronism with an interruption of a continuous transmission
of data from said calling remote party; and
f) means for notifying said information processing terminal of the
completion of said connection of said modem circuit with said information
processing terminal, and
wherein said transmission operation control means further comprises:
g) means for waiting for a transmission of a carrier from said called
remote party after connection of said modem system to said public
communication line for data transmission;
h) means for transmitting a carrier and said identification code to said
called remote party upon reception of said carrier transmitted from said
called remote party;
i) means for starting a continuous transmission of data upon reception of a
continuous transmission of data from said called remote party;
j) means for discontinuing said continuous transmission of data, and for
connecting said modem circuit connected to said public communication line
to a line leading to said information processing terminal; and
k) means for notifying said information processing terminal of the
completion of said connection of said modem circuit with said information
processing terminal.
6. An intelligent modem system as in claim 2, wherein said storing means is
adapted for storing operation mode designating information as well as said
identification code, and said modem system is provided with an operation
mode which corresponds to said operation mode designating information.
7. An intelligent modem system as in claim 6, wherein said operation mode
designating information designates whether said called remote party
communicating with said modem system over said public communication line
is required to be identified or not before connecting said modem circuit
connected to said public communication line to a line leading to said
information processing terminal.
8. An intelligent modem system as in claim 6, wherein said storing means is
adapted for storing operation mode designating information as well as said
identification code, and said modem system is provided with an operation
mode which corresponds to said operation mode designating information, and
wherein said operation mode designating information designates whether
said self-introduction is to be made or not before connecting said modem
circuit connected to said public communication line to a line leading to
said information processing terminal.
9. An intelligent modem system as in claim 8, wherein said operation mode
designating information causes said self-introduction operation only upon
occurrence of a first transmission operation in association with setting
up of said operation mode designating information, but causes said
information processing terminal to be connected to said modem circuit
without said self-introduction operation for a second transmission
operation.
10. An intelligent modem system as in claim 6, wherein said operation mode
designating information designates a telephone communication mode based on
the use of a telephone set without designating a data communication mode
based on the use of said information processing terminal after said
calling remote party is identified to be an authorized party.
11. An intelligent modem system as in claim 6, wherein said operation mode
designating information designates a transition to a telephone
communication mode based on the use of a telephone set immediately after
conclusion of data communications with said information processing
terminal.
12. An intelligent modem system as in claim 6, wherein said operation mode
designating information designates a transition to a remote maintenance
mode without designating a data communication mode based on the use of
said information processing terminal after said remote party is identified
to be an authorized party.
13. An intelligent modem system as in claim 6, wherein said operation mode
designating information designates a remote control mode without
designating a data communication mode based on the use of said information
processing terminal after said calling remote party is identified to be an
authorized party.
14. An intelligent modem system as in claim 1, wherein said verification of
said identification code is based on at least partial agreement between
said received identification code and said stored identification code.
Description
TECHNICAL FIELD
The present invention relates to an intelligent modem system which offers
improved security against unauthorized attempts to get access to the
system.
BACKGROUND OF THE INVENTION
Generally, data communication should be permitted only between authorized
parties, and it is highly desirable to eliminate any possibility of
unauthorized tapping of data from the system and sabotaging of the system
by such unauthorized access to the system. Therefore, for some time, it
has been customary to require an acknowledgment before data communication
can be started between any two parties. However, conventional modem
systems were not equipped with any such means of acknowledging the other
parties of communication, and the computer software for data communication
typically included routines for acknowledging the other parties of
communication. Therefore, communication software has tended to be more
complex than otherwise, and the users had to bear the cost for this added
complexity of the communication software.
Furthermore, since the conventional modem systems were not provided with
any means for identifying the other parties of communication, every time
data was transmitted to each modem system, the mother computer of this
modem system had to interrupt the current job by an escape sequence and
carry out the acknowledgment sequence to find out if the data was sent
from an authorized party or not. Therefore, if the incoming data was
transmitted simply by mistake or for sabotaging purpose, a considerable
time loss would be incurred to the receiver of this unauthorized data
transmission as a result of interrupting the current job, executing an
escape sequence, and recovering the status of the system.
For instance, in the case of an electronic bulletin board system, if the
bulletin board system responded to every attempt of access, the system
would be so overburdened by erroneous and other unauthorized attempts to
get access to the system that the authorized users of the bulletin board
service would have a great difficulty in receiving the service.
BRIEF SUMMARY OF THE INVENTION
In view of such problems of conventional modem systems, a primary object of
the present invention is to provide an intelligent modem system which
eliminates the need for the information processing terminal connected to
the modem system to be equipped with means to identify the other party.
A second object of the present invention is to provide an intelligent modem
system which can prevent the operation of the information processing
terminal connected to the modem system from being disrupted by attempts by
unauthorized parties to get access to the modem system.
A third object of the present invention is to provide an intelligent modem
system which can positively foil any attempts by unauthorized parties to
get access to the modem system.
These and other objects of the present invention can be accomplished by
providing a intelligent modem system which is to be connected between an
information processing terminal such as a micro computer and a public
communication line to modulate and demodulate data transmitted between the
information processing terminal and the public communication line,
comprising: information set up means which can set up at least ID
information; and reception operation control means which verifies if an
incoming call is from an authorized party or not by responding to the
public communication line according to the ID information, and connects a
modem circuit connected to the public communication line to a line leading
to the information processing terminal only when an incoming call is
confirmed to be from an authorized party.
Thus, the information processing terminal, typically consisting of a
microcomputer, connected to the modem system, may not be equipped with
means to identify the other parties of communication whereby the cost for
software for the information processing terminal may be reduced. Further,
if an attempt is made by an unauthorized party to get access to the modem
system, since the sequence for identifying the other party is carried out
by the modem system itself, and the information processing terminal may
continue the execution of the current jobs without being disrupted by any
such unauthorized incoming calls.
According to a preferred embodiment of the present invention, this modem
system may further comprise: (1) transmission operation control means
which introduces itself to the other party by responding to the public
communication line according to the ID information, and connects a modem
circuit connected to the public communication line to a line leading to
the information processing terminal upon permission of communication from
the other party; (2) means to inquire if the other party is equipped with
means to identify the other party or not, the self introduction being
performed only when the modem system of the other party is equipped with
the means to identify the other party; and/or (3) means to disconnect the
modem system from the public communication line when the other party is
not an authorized party.
According to another aspect of the present invention, the reception
operation control means is provided with the functions of: a) sending out
a carrier to the other party after connection of the system to the public
communication line in response to reception of a call from the other
party; b) receiving ID information transmitted from the other party; c)
comparing the received ID information and internal ID information; d)
starting a continuous transmission of data to the other party when the
receive ID information agrees with the internal ID information; e)
connecting the modem circuit connected with the public communication line
to a line leading to the information processing terminal in synchronism
with an interruption of a continuous transmission of data from the other
party; and f) notifying the completion of the connection of the modem
circuit with the information processing terminal to the information
processing terminal; and the transmission operation control means is
provided with the functions of: a) waiting for a transmission of a carrier
from the other party after connection of the system to the public
communication line for data transmission; b) transmitting a carrier and ID
information upon reception of the carrier transmitted from the other
party; c) starting a continuous transmission of data upon reception of a
continuous transmission of data from the other party; d) discontinuing the
continuous transmission of data, and connecting a modem circuit connected
to the public communication line to a line leading to the information
processing terminal; and e) notifying completion of the connection of the
modem circuit with the information processing terminal to the information
processing terminal.
According to yet another aspect of the present invention, the information
set up means is adapted for setting up operation mode designating
information as well as ID information, and the modem system is provided
with an operation mode which corresponds to the operation mode designating
information.
The operation mode designating information may designate: (1) whether the
other party is required to be identified or not before connecting the
modem circuit connected to the public communication line to a line leading
to the information processing terminal; (2) whether self introduction is
to be made or not before connecting the modem circuit connected to the
public communication line to a line leading to the information processing
terminal; (3) a telephone communication mode based on the use of a
telephone set without designating a data communication mode based on the
use of the information processing terminal immediately after the other
party is identified to be an authorized party; (4) a transition to a
telephone communication mode based on the use of a telephone set
immediately after conclusion of data transmission with the information
processing terminal; (5) a transition to a remote maintenance mode without
designating a data communication mode based on the use of the information
processing terminal immediately after the other party is identified to be
an authorized party; or (6) a remote control mode without designating a
data communication mode based on the use of the information processing
terminal immediately after the other party is identified to be an
authorized party.
According to yet another aspect of the present invention, the operation
mode designating information causes the self introduction operation only
upon occurrence of a transmission operation in association with setting up
of the operation mode designating information, but causes the information
processing terminal to be connected to the modem circuit without the self
introduction operation for a normal transmission operation, and the
verification of the ID information is based on at least partial agreement
between the received ID information and the internal ID information, for
instance, by using a wild card digit.
BRIEF DESCRIPTION OF THE DRAWINGS
Now the present invention is described in the following with reference to
the appended drawings, in which:
FIG. 1 is a block diagram of an embodiment of the intelligent modem system
according to the present invention;
FIG. 2 is a flow chart of a part of the control program of the embodiment
shown in FIG. 1 which is primarily related to the registration of ID
numbers;
FIG. 3 is a flow chart of another part of the control program which is
related to the protocol for the process of ID exchange;
FIG. 4 is a flow chart of yet another part of the control program which is
related to the change-over of the operation mode through a command
character;
FIG. 5 is a flow chart of yet another part of the control program which is
primarily related to the ID verification routine;
FIG. 6 is a time chart illustrating the timing of data transmission and
reception preceding the onset of the state of data transmission;
FIG. 7 shows a data format for information exchange;
FIG. 8 shows how information fields are defined;
FIG. 9 shows a signal format used in the invention;
FIG. 10 shows another signal format used in the invention; and,
FIG. 11 shows the meaning of the information fields for each of the signals
illustrated in FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a block diagram illustrating the electric hardware structure of
this modem system. This modem system is connected to a public
communication line or the TEL line via a communication transformer 1, and
to an information processing terminal (which is referred to as DTE
hereinafter) 3, such as a mother computer, via an RS232C interface 2.
Between the communication transformer 1 and the RS232C interface 2 are
provided a hybrid circuit 4, a modem LSI 5, and a full duplex serial IO
port 6, in that order. The hybrid circuit 4 serves as a driver/receiver,
and the modem LSI 5 is provided with various functions which can be
selected by external control signals as well known. For instance,
selection of a modulation system FSK (300), PSK (1,200) or QAM (2,400),
selection of a communication speed 300 bps, 1,200 bps or 2,400 bps,
adjustment of the volume level of an internal speaker, on-off control of
the echoing of the transmitted data, on-off control of a monitor speaker
7, on-off control of the abort timer, etc. are possible with the modem LSI
5.
The overall operation of this modem system is controlled by a microcomputer
which comprises a CPU 9, ROM 10 and RAM 11.
The serial IO port 6 is of a full duplex type, and is capable of switching
over the modem LSI 5 between the DTE 3 (the transparent mode) and the CPU
9 (the command mode) as well as of performing serial/parallel conversion.
A telephone set can be connected to the TEL line via a current sensor 8
which forms a part of this intelligent modem system. The CPU 9 receives
various commands from the DTE 3 via the serial port 6, and, via an OF
terminal of a parallel IO port 12, on-off controls a switch SW for
selectively connecting the modem system to the TEL line. The output of the
current sensor 8 is supplied to the CPU 9 via a TK terminal of the
parallel IO port 12 so that the CPU 9 can detect the use of the telephone
set when a call is placed from this telephone set or an incoming call is
received by the telephone set. The CPU 9 can further send out a CD signal
to the DTE to indicate the start of data communication, via the parallel
IO port 12.
FIGS. 2 through 4 show a flow chart of the control program which is
executed in the CPU 9. Now the operation of the present embodiment is
described in the following with reference to this flow chart.
When the execution of the program is started, for instance, by turning on
the supply of electric power to the modem system, various flags and
registers are initialized in step 201, and the input buffer for storing
the command from the DTE 3 is cleared in step 202. Thereafter, the system
waits for the arrival of a call by monitoring the status of the parallel
IO port 12 in steps 203 and 204, and key entries from the keyboard of the
DTE 3 by monitoring the status of the serial port 6 in steps 205 and 206.
When any key entry from the keyboard of the DTE 3 is detected in this
condition o when the determination result is "yes" in step 206, the data
entered from the DTE 3 is sequentially written into the input buffer in
step 208 until a CR code or a carriage return code is entered in step 207.
When a CR code is detected in step 207, a command determination process is
conducted in step 209 according to the data stored in the input buffer.
Thereafter, it is determined whether the command entered from the DTE 3 is
an auto dial command (ATD) "yyy . . . y" in step 210, an ID registration
command (ATJ) "xxxxxx" in step 211, or an ID exchange command (ATJ1) in
step 212.
When an entry of the ID registration command (ATJ) "xxxxxx" is detected in
step 211, the command character at the head of the entered string and the
subsequent five ID digits are transferred to the designated areas of the
RAM 11, which is provided with a back-up battery, in step 213. When an
entry of the ID exchange command (ATJl) is detected in step 212, "1" is
set to the flag J, which indicates the selection of the ID exchange
function in step 214. In this way, according to the command from the DTE
3, a command character and five ID digits, and the flag J for the ID
exchange function can be set up.
When the auto dial command (ATD) "yyy . . . y" is transmitted from the DTE
3 in step 210 or an incoming call is detected via the parallel IO port 12
in step 204, the process of data transmission or data reception is
executed, as the case may be, as given by the part of the flow chart of
FIG. 3 where data exchange between two identical modem systems is
considered.
First of all, the modem system acting as the sender sets its flag I for
indicating whether the J option is being selected, to "0" in step 215.
This J option is set up by a J option assign command (ATD) "yyy . . . yJ",
in the similar way as in step 212, to execute the ID exchange function for
only once even when no ID exchange function has been set up. By this J
option, it is possible to communicate with a conventional modem system not
equipped with any ID exchange function without creating any compatibility
problems as well as to execute an ID exchange sequence when the other
party is equipped with a similar ID exchange function.
Thus, when the J option assign command (ATD) "yyy . . . yJ" is received
from the DTE 3 in step 216, the flag I is set to "1" in step 217.
Thereafter, the sender modem system turns on the switch SW by setting up
off-hook information in the parallel IO port 12 in step 218, and feeds an
auto dial command to the modem LSI 5 in step 219. Meanwhile, the receiver
modem system sends out off-hook information to the parallel IO port 12 and
thereby turns on the switch SW in step 232. As a consequence, an answer
tone is produced from the modem LSI 5 and a carrier is transmitted
thereafter as shown in FIG. 7. This in turn causes the receiver modem
system to confirm the carrier from the sender modem system and returns a
carrier to the sender modem system.
Once the two modem systems have sent carriers to each other, the two modems
systems confirm the complete connection between them in steps 220 and 221
or steps 233 and 234, and, thereafter, the ID exchange routine is
conducted in mutual synchronism as shown in FIG. 7.
In an initial stage of the ID exchange sequence, as shown in FIG. 8, an
inquiry INQ including a version number to identify the other party is sent
from the sender ORG to the receiver ANS according to the data format given
in FIG. 10 in step 223, and the sender waits for the arrival of a reply
IAN including a version number from the receiver in step 224. The receiver
modem system thus waits for the inquiry INQ including a version number
from the sender in step 236, and, upon arrival of this inquiry INQ,
returns a reply IAN including a version number to the sender in step 238.
FIG. 11 illustrates the information field content for the signals used in
the ID exchange sequence.
In this way, only when compatibility between the two systems is confirmed
by the agreement of the version numbers, the sender sends out its ID
number to the receiver in step 226. Therefore, according to the present
embodiment, even when the receiver happens to be a conventional modem
system which is not equipped with such an ID exchange function, the risk
of the sender inadvertently sending out its ID to the receiver and thus
disclosing its ID number to an unauthorized party can be positively
prevented. When no IAN is returned within a certain prescribed time
interval after an inquiry including a version number is made by the sender
in step 223, a monitor timer runs out in step 225 and the TEL line is
immediately disconnected from the modem system thereby preventing
unnecessary line charges from being incurred. Likewise, if the receiver
fails to receive an INQ including a version number within a prescribed
time interval, its monitor timer runs out in steps 237 and the TEL line is
immediately disconnected thereby preventing unnecessary line charges from
being incurred. Such an automatic disconnect feature is effective in
preventing an electronic bulletin board from being occupied by
unauthorized parties and thereby limiting the availability of the service
to authorized parties or legitimate subscribers.
If it is determined in step 222 or step 235 that an ID exchange is not
necessary, the step of ID exchange is bypassed and the state of the system
directly moves on to that for data communication. In this way, the modem
system according to the present invention can communicate with
conventional modem systems which are not equipped with any ID exchange
function by omitting the ID exchange sequence.
When the compatibility of the other modem system has been confirmed, the
sender introduces itself to the receiver by sending out its ID number in
step 226, and waits for the acknowledgment ACK from the receiver in step
227. After receiving the ID number of the sender in step 239, the receiver
verifies that the sender is indeed an authorized party by matching the
received ID number with an internal ID number in step 240. According to
the present embodiment, the internal ID number may contain a wild card
digit "*" in any one of the five digits it contains so as to create a
certain tolerance on that particular digit. Thus, as shown in the part of
the flow chart given in FIG. 5, in this ID number verification routine,
each digit is verified either from the top most place or lower most place
in sequential manner in steps 301, 302, 303 and 304. If any mismatch is
detected during these verification steps in step 303, the flag L is reset
to "0" as a case of mismatch and the ID number verification routine is
concluded. However, when the wild card digit "*" is involved (step 302),
there is no possibility of mismatch, and the system flow advances to the
verification of the next digit. When all the digits have been verified in
this way in step 301, the flag L is set to "1" as a case of successful ID
number verification in step 305.
According to such an ID number verification routine, it is not necessary
for all the subscribers to have a same ID number when a wild card digit is
assigned to one or more digits in the internal ID number. For instance,
when this system is applied to an electronic bulletin board system, the
system can offer service to a large number of subscribers. Thus, since
different ID numbers can be assigned to different subscribers, security
may be ensured and, if desired, different services may be offered to
different subscribers depending on their ID numbers.
When the ID number verification sequence has been concluded by the receiver
modem system in step 240, it immediately sends back an acknowledgment
signal to the sender modem system in step 241. On the other hand, the
sender modem system, upon reception of acknowledgment signal ACK from the
receiver modem system in step 227, waits for a prescribed string of data
in step 228. After sending out the acknowledge signal in step 241, the
receiver modem system starts sending out the prescribed string of data in
step 242. This string may consist of characters arranged in a well define
pattern such as 123123123 . . .
When such a string of data is received by the sender modem system in step
228, the sender modem system starts sending a similar well defined string
of data in step 229. In the receiver modem system, after it has started
sending out the string of data and has started receiving the similar
string of data from the sender modem system in step 243, the receiver
modem system discontinues the sending out of the string of data in step
244 and waits for the cessation of the transmission of the string of data
from the sender modem system in step 245. In the sender modem system, upon
detection of interruption of the string of data from the receiver modem
system in step 230, the sender modem system immediately stops sending out
the string of data, and proceeds to the state of data communication or to
the transparent mode in synchronism thereto in step 231.
Meanwhile, in the receiver modem system, upon detection of the cessation of
the string of data from the sender modem system in step 245, the receiver
modem system likewise immediately stops sending out the string of data and
proceeds to the state of data communication or to the transparent mode in
synchronism thereto.
In this way, by carrying out the protocol in steps 218 through 231 or steps
232 through 245, the sender and receiver modem systems can substantially
simultaneously proceed to the state of data communication as shown in FIG.
7, and the possibility of revealing any ID information due to any large
shifting between the two parties in the timing of entering the state of
data communication can be positively prevented.
In this way, when synchronism has been established between the two parties,
according to the present embodiment, prior to the transition to the
transparent mode for data communication, the system may start operating in
one of a number of modes of operation depending on the state of the ID
agreement flag L and the content of the command character shown in FIG. 9.
In other words, as shown in FIG. 4, when a disagreement is detected between
the ID numbers in step 246, on-hook information is immediately sent to the
parallel IO port 12 in step 258. As a result, the switch SW is turned off
to disconnect the modem system from the TEL line, and a CD signal is
produced from the parallel IO port 12, whereby the DTE 3 can detect the
disabling of data communication.
On the other hand, when a complete agreement between the ID numbers is
detected in step 246, depending on the content of the command character
(FIG. 9), it is determined whether the data communication mode (command
character I), the talk mode subsequent to data communication (command
character T), the talk mode (command character S), the remote maintenance
mode (command character M) or the remote control mode (command character
R) is being selected in steps 247, 248, 249, 250 and 251.
When the data communication mode is determined to be the case in step 247,
the flag K for the talk mode subsequent to data communication is reset to
"0" in step 252, and a CD on signal is transmitted to the DTE 3 via the
parallel IO port 12 in step 253. At this point, permission to start data
communication is notified.
According to the CD signal, the DTE 3 can determine whether data
communication may be started or not, and the serial port 6 accomplishes
the switch over between the DTE 3 and the modem LSI 5 to achieve the
transparent mode. Thereafter, the data sent form the DTE 3 is sent to the
modem LSI 5 via the serial port 6, and is ultimately transmitted to the
TEL line. Meanwhile, the data arriving from the TEL line can reach the DTE
3 via the serial port 6 in step 254.
The CPU 9 then waits for the conclusion of data communication in step 255.
If conclusion of data transmission is confirmed in step 255, provided that
the flag K is not "1" in step 256, the flags I and K are set to "0" in
step 257, on-hook information is sent to the parallel IO port to turn off
the switch SW in step 258, and CD signal off information is sent to the
parallel to IO port in step 259, to notify the DTE 3 the conclusion of
data transmission in step 259.
On the other hand, the talk mode subsequent to data communication is
determined from the content of the command character in step 248, the flag
K is set to "1" in step 260. Thereafter, the sequence from the sending out
of the CD signal and the confirmation of the conclusion of data
communication is performed in steps 253 through 255, and, upon confirming
of the conclusion of data communication in step 255, since the flag K is
determined to be "1" in step 256, the talk mode is produced in step 261.
In this talk mode, as shown in FIG. 6, a carrier off signal is given to the
modem LSI in step 307, and a monitor speaker on signal is supplied to the
modem LSI in step 308.
Thereafter, the status of the parallel IO port is read out in step 309, and
the system waits for the start of the telephone communication while
monitoring the output from the current sensor 8 in step 310. Upon
detection of the start of telephone communication in step 310, a monitor
speaker off signal is supplied to the modem LSI in step 311. Then, the
conclusion of telephone communication is detected in step 313 according to
the status of the serial IO port in step 312, and the talk mode processing
routine is concluded upon detection of telephone communication in step
313.
Thereafter, the steps 257 through 259 are executed, and the execution of
the control program is concluded.
When the remote maintenance mode (step 250) or the remote control mode
(step 251) is determined according to the content of the command
character, the remote maintenance routine (step 262) or the remote control
routine (step 263) is executed as the case may be, in well known fashion
in either case. Thus, it is made possible to perform remote maintenance of
the modem system of the other end or to control external equipment via a
microcomputer or the like which is connected to the modem system of the
other end.
Thus, by using the intelligent modem system of the present invention in
both the sender and the receiver, the verification of the other parties
can be performed at high speed without any burden on the information
processing terminals such as microcomputers associated with the modem
systems. Therefore, the communication software may not be provided with
any verification routine, and the information processing terminals such as
microcomputers are not all distracted by unauthorized attempts to get
access to the modem system.
In the above embodiment, the ID number was transmitted from the sender to
the receiver, but it is equally possible for the ID number to be
transmitted from the receiver to the sender, or to be exchanged between
the sender and the receiver. Likewise, although in the above embodiment,
the exchange of an ID number was performed both upon reception and
transmission of data, but the ID exchange may be performed only upon
receipt of data if the user is interested only in eliminating the
inconveniences which may arise due to unauthorized attempts to get access
to the modem system.
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